1. Field of the Invention
The present invention relates to an imaging device (image pickup device) and an image analysis method that can analyze a movement of a ball from an image in a frame captured by an image pickup means using a rolling shutter system.
2. Description of Related Art
A speed-gun is well known as a device for measuring a speed of a ball used for a sport such as baseball, tennis, and the like.
A speed-gun measures the Doppler effect of reflected waves from a ball, for example, and estimates a ball speed. Therefore, such a speed-gun has to be placed along a movement direction of the ball and thus there is high risk of collision with the ball. In addition, there is a problem that it is difficult to confirm at which position of the moving ball the speed was measured.
For the purpose of avoiding such a collision with a ball, a method for measuring a speed of a moving ball by capturing an image of a ball from a direction orthogonal to the moving direction and analyze the image is disclosed (JP2001-264016A, Patent Document 1, for example). The technique disclosed in the document is as follows. When an impact on a ball is detected by a trigger sensor, a mechanical shutter repeatedly opens and shuts while a flash unit fires repeatedly in synchronism with the movement of the shutter so as to capture multiple ball images in an image frame using a CCD camera.